The invention relates to a new molding technique for rapid tooling that can be used to provide high precision, low shrinkage articles that require very little machining or other finishing. The invention specifically relates to a method of making such articles or products by forming a green article in a new way, and also to an apparatus and method for infiltrating the green article with a molten metal after removing moisture and binder from the green article.
The field of rapid tooling deals with methods to reduce the time required for producing a tooling component compared to traditional machining. Within this context, tooling or tools refer to mold cavities as well as machine elements used in manufacturing. Most injection molding, die-casting, stamping, and other industrial molding processes have high costs associated with tooling production.
A number of US patents seek to provide solutions to these disadvantages. U.S. Pat. No. 5,851,686 discloses the use of a gating means in combination with a spontaneous infiltration process to produce a metal matrix composite body. In particular, a permeable mass of filler material or a preform is spontaneously infiltrated by molten matrix metal to form the metal matrix composite body. A gating means is provided which controls or limits the areal contact between molten matrix metal and the filler material or perform in an attempt to result in less machining of a formed metal matrix composite body compared with a similar metal matrix composite body made without a gating means. The use of a gating means also allegedly ameliorates the tendency of a formed metal matrix composite body to warp due to the contact between the formed composite body and matrix metal carcass.
U.S. Pat. No. 6,224,816 discloses a tool having a molding surface formed from a flowable material (e.g., powder material) wherein the shape of molding surface is formed from a molding process using a master pattern having a surface with a shape substantially the same as the shape of the molding surface to be formed. The tool has at least one thermal control element located within it and spaced from the molding surface where a component used in forming the thermal control element is located within the flowable material prior to solidifying the material. The powder material is preferably a mixture of metals and the thermal control elements include fluid flow paths, heating elements, temperature sensors, and the like.
U.S. Pat. No. 6,399,018 discloses a multi-step forming, debinding, sintering and infiltrating process for making solid objects using a metal-ceramic composition. In this process, the mixture is held for a period of time to degas and settle the powdered material from a liquid binder. The packed geometry is then heated to above the melting temperature of the binder to remove the binder portion of the solid geometry. Upon removal of the binder the binder-free solid geometry is raised to a temperature where the metal pre-sinters together into a three-dimensional rigid matrix with interconnected porosity to form a solid precursor. The porous matrix includes the particulate ceramic material and a first metal, which are at least partially sintered. A molten second metal is then introduced to the fill the porous matrix and form an infiltrated matrix. In addition to speed of production, improvements associated with this method allegedly include a solid object having improved thermal conductivity, hardness, wear resistance and reduced shrinkage as compared with the rapid tooling techniques taught in the prior art.
U.S. Pat. No. 6,502,623 discloses a process for making a metal-matrix composite that includes a mixture of particulate ceramic powder with a liquid carrier, without addition of a binder, to prepare a slip having thixotropic properties. The slip is introduced in a substantially dense consistency into a casting mold which is then subjected to vibrations so as to separate the carrier from the ceramic particles and to allow the carrier to float upon the ceramic particles while at the same time compacting the slip to realize a ceramic preform of porous consistency having pores. After terminating the exposure of the casting mold to vibrations, the liquid carrier is removed and the preform is allowed to solidify in the casting mold, without exposure to any further compaction measures, such as sintering, pressing or the like, and the casting mold is maintained in a position of rest. Subsequently, matrix metal is poured into the casting mold to fill the pores of the preform.
As described in these patents, the field of rapid tooling has brought increased speed to producing prototype parts and molds, but further improvements are desirable and necessary in order to reduce the time and number of steps required to take a computer generated model to production tooling and then to actual part production. The present invention now provides such improvements.